A coordinated program of physiological and morphological experiments is planned to acquire greater understanding of the events involved in the development and specification of synaptic connections, and the factors governing the inductive and tropic influences of the developing nerve on the postsynaptic membrane. Electrophysiological experiments are performed on identified developing nerve-muscle junctions and followed by electron microscopy of the same nerve terminal. The primary aims of the proposed experiments are: (1) To investigate the physiological properties of developing nerve-muscle junctions, specifically analyzing the mechanisms of the terminal's transmitter release properties and the terminal's physiological and morphological maturation during ontogeny; (2) To examine the inductive role of the developing nerve terminal on the acetylcholine receptor distribution, acetylcholinesterase enzyme localization, and the morphological specialization of the postsynaptic membrane; (3) To analyze the factors which govern the specificity of synaptic connections on developing muscle fibers.